1. Field of the Invention
The present invention relates to a chalk adhesion polymer latex, comprising acrylates and methacrylates, and its method of preparation from a monomer composition. The polymer latex can be blended with vinyl acetate/acrylic copolymer coatings to form a finished latex coating composition with improved chalk adhesion properties.
2. Description of the Prior Art
Chalking has been defined as the formation of a friable powder on the surface of a paint film, caused by the disintegration of the binding medium due to disruptive factors during weathering. Chalking resistance is the ability of a coating to resist the formation of a friable powder on the surface of its film caused by the disintegration of the binding medium due to degradative weather factors.
One of the principal problems encountered in the formulation of paints, especially exterior house paints, is the improvement of chalk adhesion properties. An exterior paint coating with good chalk adhesion properties has the ability to penetrate a chalky coating, such as weathered paint, and to adhere to the surface beneath the chalky coating.
One of the primary uses for alkyd resins as components of water-based coatings is the modification of exterior latex house paints. Oleoresinous modifiers have been favored for this purpose because many paint manufacturers and users seek the added adhesion properties that alkyds impart to exterior formulations. Acrylic emulsions normally afford good adhesion to chalky surfaces under moderate exposure conditions, but under severe conditions failures can occur. Alkyds have therefore been employed in exterior latex paints to provide an extra safety factor of added adhesion.
However, alkyds also have shortcomings. While fully cured alkyds can provide an acrylic paint with extra adhesion on certain problem substrates, they adversely affect the fast-dry characteristics of the acrylic. An alkyd generally requires several days, the number varying with ambient conditions, to dry to a full cure and to develop optimum adhesion and blister resistance. As a result, an alkyd-modified paint has a greater chance of failure should inclement weather occur during the first few days following application. Even without rain, prolonged tackiness can provide sites for early dirt pickup.
Alkyd modification can also make acrylic latex paints more susceptible to the damaging effects of exposure. Tests have shown that the durability of modified paints decrease as the level of alkyd modification increases. Both tint retention and chalk resistance diminish because the alkyd breaks down rather rapidly on exposure. Also, problems in paint manufacture and storage can arise because the alkyd can absorb the surfactants and dispersants used for stability in the formulation. These and other problems related to alkyd modification are well known. See Mattei et al, "Chalk Adhesion Polymer for Exterior House Paints", RESIN REVIEW, vol. 24, no. 4, pages 14-22 (April 1975).
U.S. Pat. No. 4,504,609 to Kuwajima et al discloses an aqueous coating composition comprising a resinous vehicle composed of at least one aqueous resin and at least one water insoluble component. The aqueous resin can be polyester, alkyd, acrylic, acryl-modified polyester, and acyl-modified alkyd. The water insoluble resinous component is obtained by polymerization or copolymerization of alpha, beta-ethylenically unsaturated monomers.
U.S. Pat. No. 4,529,765 to DenHartog et al discloses a coating composition containing about 20-80 percent by weight of a binder and 80-20 percent by weight of a solvent for the binder. The binder comprises an acrylic amino ester polymer of polymerized monomers of methyl methacrylate and monomers of alkyl methacrylate or alkyl acrylate, and an acrylate polymer having pendent polymerizable ethylenically unsaturated groups.
U.S. Pat. No. 4,199,400 to Bakule et al discloses migration-resistant binder compositions mixed with an anionically stablized polymer latex and a volatile base.
U.S. Pat. No. 3,454,516 to Victorius discloses coating compositions comprising soft phase polymers which have infused or dissolved in them hard phase polymers.